1. Field of the Invention
This invention relates to a novel ion modulating electrode which forms an electrostatic image on a charge receptor by modulating the ion flow.
2. Description of the Prior Art
There are two methods of electrostatic recording that have been practiced conventionally. One is a direct discharge recording in which multi-stylus electrodes are used and a direct discharge takes place between the dielectric charge receptor surface and the electrode. The other is an indirect discharge recording in which a discharge is made to take place at a point remote from the charge receptor surface and the generated ions are used for forming the latent image.
The direct discharge recording method has disadvantages in that the charge receptor surface is liable to damage due to contact with the multi-stylus electrode and in that the distance between the multi-stylus electrode and the charge receptor surface should be kept to a required amount with high precision.
On the other hand, the indirect discharge recording method makes it possible to expand greatly the distance between the multi-stylus electrode and the charge receptor surface because a stable discharging can be performed at a point distant from the charge receptor surface to produce ions which will be attached to the charge receptor surface. Thus with this method the accuracy of the distance is allowed to be not so severe as in direct discharge recording, making it easy to handle the device of this method. Therefore, various kinds of recording electrodes have been proposed for use with the device of this method.
A Japanese Patent Laid-Open Application No. 3533/1979 proposes a latent image forming electrode which is improved on the problems experienced with conventional recording electrodes, such as difficulty in manufacturing the electrode, clogging of apertures and difficulty in controlling the dot diameter expansion.
The latent image forming electrode of the above patent application consists of two conductors for producing ions by discharge with a dielectric member bonded between the two conductors and a third conductor for ion-modulating with a dielectric member bonded between the third conductor and one of the above two conductors thus forming a multi-layer structure. This multi-layer electrode has through-apertures.
With this electrode, a pulse voltage is applied between the two conductors, which are exposed at the inner wall of the through-apertures, to cause a discharge between the electrodes to produce ions. The flow of ions to the charge receptor surface is controlled by applying a pulse voltage to the control electrode. It was reported that the above construction greatly improved the recording speed enabling high-speed recording.
The above electrode, however, has disadvantages in that a large amount of current flows to the electrode because the electrode is exposed and in that since high energy electrons and positive and negative ions are generated near the electrode, the electrode is liable to be corroded, shortening its life and deteriorating the efficiency of ion generation.
Other type of electrode is proposed in the U.S. Pat. Nos. 4,155,093 and 4,160,257. The American patented electrode is described in the following referring to FIG. 1.
In the figure, reference numerals 1 and 2 denote electrodes between which a dielectric 4 is disposed. AC voltage from an AC power source 8 is applied between the two electrodes. A voltage from a power source 10 is applied between a backing electrode 7 of a recording member 6 and a modulating electrode 3 which is bonded to the electrode 2 with a dielectric 5 held therebetween. Also a voltage from a power source 9 is applied between the backing electrode 7 and the electrode 2. The application of voltage between the electrodes 1 and 2 causes a spark discharge producing ions, of which only positive or negative ions are accelerated toward the recording member 6.
This electrode has an advantage that since the spark discharge occurs between the electrodes through the dielectric 4, the damage to the electrodes caused by discharge is very small. There are, however, various problems that have to be solved before it can be put to practical use. For example, apertures are liable to be clogged because the through-apertures formed in the electrode 2 are closed at one end by the dielectric 4 and it is difficult to clean the through-apertures; the dielectric itself hinders the flow of ions to the recording member 6, making it necessary to provide a means to heighten the ion density.